The present invention generally relates to electroetching and, more particularly, to the electroetching of relatively large area masks having high density features for the fabrication of microelectronic components.
Chemical etching is well known in the art for making metal masks suitable for use in the fabrication of microelectronic components. Chemical etching frequently employ highly corrosive and hazardous reagents. Such processes also produce toxic wastes requiring very expensive treatment to meet the increasingly stringent environmental laws. Furthermore, the chemical etching process is slow and has limited resolution. Electroetching techniques reduce the severity of such concerns but have not been used for making metal masks.
Electroetching additionally offers better control over metal removal than does chemical etching. Compared to chemical etching which generally is isotropic, a certain degree of anisotropy can be achieved with electroetching. Due to the shadow effect of photoresist used to define the areas to be etched, there is some restriction to the direct access by the current in these locations whereby etch rates are locally reduced and a degree of anisotropic etching effect is produced. Other advantages of electroetching include high metal removal rate and the possibility of etching varieties of metals and alloys, including corrosion resistant metals, in electrolytes with minimized safety and waste disposal problems.
U.S. Pat. No. 3,962,056 issued on Jun. 8, 1976 to Shakir A. Abbas, discloses a modified electroetching process for forming holes with vertical sides in a masked monocrystalline silicon wafer. Impurities are introduced through registered mask openings on both sides of the silicon wafer. The wafer then is anodically etched through mask openings on one side of the wafer to form porous silicon regions completely through the wafer at the locations of the openings. The resultant porous silicon regions are removed with a porous silicon etchant simultaneously applied through the mask openings to both sides of the wafer.
U.S. Pat. No. 3,730,861 issued on May 1, 1973 to W. A. Haggerty teaches another electroetching technique intended to produce precisely shaped workpieces. The technique positions an electro-chemical machining tool at a preset distance from a rotating anodic workpiece while directing a stream of cathodic electrolyte against the workpiece.
Neither of the exemplary cited patents addresses the fabrication of metal masks by electroetching and the problems thereof of maintaining uniformity of current and electrolyte distribution over the workpiece, especially where the workpiece is a relatively large area mask having high density features for the fabrication of microelectronic components.